1. Field of the Invention
The invention relates to a fuel pressure sensor abnormality diagnosis apparatus for diagnosing an abnormality of a fuel pressure sensor for detecting a pressure of fuel supplied to a fuel injection valve of an internal combustion engine.
2. Description of Related Art
A fuel pressure sensor abnormality diagnosis apparatus for diagnosing an abnormality of a fuel pressure sensor for detecting a pressure of fuel supplied to a fuel injection valve of an internal combustion engine is known (see Japanese Patent Application Publication No. 2007-138774 (JP 2007-138774 A), for example). The apparatus (hereinafter referred to as “conventional apparatus”) makes a provisional diagnosis that the fuel pressure sensor is abnormal when a difference between a maximum value and a minimum value of a detected value of the fuel pressure that is detected by the fuel pressure sensor (hereinafter simply referred to as “detected value”) is below a predetermined value and an intermediate value between the maximum value and the minimum value is deviated by a predetermined value or more from a target value for a predetermined period.
Further, in the case where the detected value is greater than the target value when making the provisional diagnosis, the conventional apparatus decreases a fuel discharge amount of a fuel pump for supplying fuel to the fuel injection valve. On the other hand, in the case where the detected value is less than the target value when making the above provisional diagnosis, the conventional apparatus increases the fuel discharge amount of the fuel pump. In the case where a change amount of the detected value is below a predetermined amount for a predetermined period from when the fuel discharge amount is decreased or increased as such, the conventional apparatus makes a formal diagnosis that the fuel pressure sensor is abnormal.
However, in the internal combustion engine recited in JP 2007-138774 A, the fuel discharge amount of the fuel pump is feedback controlled such that the detected value coincides with the target value. Therefore, if a state where the detected value is less than the target value continues for a relatively long time, there is a possibility that the fuel discharge amount of the fuel pump reaches its maximum amount. Therefore, there is also a possibility that the fuel discharge amount of the fuel pump reaches its maximum amount and the detected value is less than the target value while the conventional apparatus makes the provisional diagnosis.
In this case, after the conventional apparatus makes the above provisional diagnosis, the fuel discharge amount cannot be increased even if it shall be increased in order to make the formal determination, and thus the conventional apparatus can not make the formal diagnosis. Therefore, in the conventional apparatus, when the fuel discharge amount of the fuel pump reaches its maximum amount and the detected value is less than the target value, it cannot diagnose the abnormality of the fuel pressure sensor.